Ford
Type:
    Powertrain - Fuel and Air Metering - ISO/SAE Controlled
Description:
    MAF Sensor Circuit Low Conditions
Cause:
    DTC P0505 not set Engine running, then the PCM detected a MAF sensor signal of less than 0.23v Check for leaks at air outlet tube and for loose tube clamps

Generic
Type:
    Powertrain - Fuel and Air Metering - ISO/SAE Controlled
Description:
    Mass or Volume Air Flow "A" Circuit Low

GM
Type:
    Powertrain - Fuel and Air Metering - ISO/SAE Controlled
Description:
    MAF Sensor Circuit Low Frequency Conditions
Cause:
    Engine runtime over 2 seconds, engine speed more than 300 rpm, system voltage more than 10v, throttle position less than 50%, then the PCM detected that the MAF sensor input was 10 hertz or less (less than 300 Hz on 7.4L), condition met for over 250 ms.

Nissan
Type:
    Powertrain - Fuel and Air Metering - ISO/SAE Controlled
Description:
    Mass air flow (MAF) sensor - voltage low
Cause:
    Wiring, MAF sensor, air leak, ECM